This metal lid, for which a new process to make the pressure release hole was created, with a removable seal, the removal of which allows the easy opening of the container, by the elimination of the internal vacuum of the container, is formed by a metal lid of the common, known type, usually made of aluminium or iron sheet plate, constituted by a circular panel with a downward turned rim, having, along its inner peripherial circumference, a circular groove containing a sealing gasket, made of a resin-like material, such as "plastisol" or other similar material, used to create a type of seat on the rim of the glass or of the other glass container, with said metal lid not being part of this invention.
This type of metal lid has been used, normally, to seal glass containers to pack different foodstuff, and the sealing being achieved by beading and by the use of special clamps, with such a system requiring the use of thick-walled glass containers, and, also, such containers having a beading in its rim, in order to co-operate with the downward rim of the lid, during the beading process, a process that, besides being uneconomic, due to the use of larger quantities of material for the containers, harms its visual aspects, due to the heavy appearance, which is not proper for the later use of the container as a common water glass, a use which is a sale promotion for the product.
With the improvement and evolution of such type of packings, namely, those containers formed by glass tumblers, their sealing has been normally achieved by vacuum, in other words, the vacuum formed within the packing container is used as a sealing element and lid fixing element, for its air-tight sealing, therefore excluding the use of clamps and beading machines, this being a considerable improvement for such glass containers, mainly those shaped as tumblers, for they were not subject to the pressure and impact of beading clamps any more, and with the containers being made with relatively thin walls, eliminating the need of a heavy rim or bead at the open mouth, offering them a better look and the best possibility of being used as domestic drinking glasses, with the same conditions of the glass tumblers made for drinking purposes.
However, even considering the new sealing system of a metal lid as more economic and offering a better look to the packed products, offering the opportunity of a later use of the glass container as a drinking glass, it still requires, for the opening or removal of the lid, the use of a pointed instrument, such as a pointed knife, to be introduced under said rim or skirt of the metal lid, in order to achieve the elimination of vacuum and the total opening or removal of the lid, and such an operation not only makes it difficult to open the packings, but may create a possible hazard to the operator's hands.